Generally, light-emitting diode (LED) structures have a light-emitting layer interposed between a lower layer and an upper layer, wherein the upper layer and the lower layer have an opposite type of conductivity forming a p-n junction. The radiative recombination of electron-hole pairs in the depletion region of the p-n junction causes the emission of electromagnetic radiation (e.g., light). The electromagnetic radiation may be in the visible range or may be in a non-visible range. Different colors of LEDs may be created by using materials with different band gaps. Further, an LED with electromagnetic radiation emitting in a non-visible range may direct the non-visible light towards a phosphor lens or a like material type. When the non-visible light is absorbed by the phosphor, the phosphor emits a visible light.
The light-emitting layer typically emits light from both sides of the light-emitting layer. In practice, however, applications frequently only require light emitted from a single side, and because light is emitted from both sides, some light energy is lost. In an attempt to increase the amount of light emitted from a single side of the LED device, a reflective layer has been formed between the substrate and the LED structure. The reflective layer comprised a metal reflective material that acted to reflect light emitted from the LED structure on the substrate side back towards the light-emitting face of the LED device, thereby increasing the light efficiency of the LED device.
While the reflective metal layer is sufficient for some applications utilizing longer wavelengths, it has been found that the reflectivity of the metal layer is low for shorter wavelengths. As a result, the light efficiency of LED structures using a metal reflective layer is lower than desired. Accordingly, there is a need for an LED device having an increased light efficiency.